Answer:
The value of y = 4
Explanation:
Explanation:-
Given the operation *is defined by
 x*y=2 x-y,where x and y are real numbers
Given y * ( 3 * y ) = 6
 ⇒ y * ( 2 (3) -y) = 6 (∵ x*y=2 x-y)
 ⇒ y * ( 6 - y) = 6
 ⇒ 2 (y) - (6 - y ) = 6
 ⇒ 2 y - 6 + y = 6
 ⇒ 3 y = 6 + 6
 ⇒ 3 y = 12
 ⇒ y = 4
Verification:-
Put y =4 in given operation
 L.H.S 
 y * ( 3 * y ) = 4 * ( 3 * 4)
 = 4 * (2(3)-4) (∵ x*y=2 x-y )
 = 4 * ( 6-4)
 = 4 * 2 
 = 2(4) -2 (∵ x*y=2 x-y )
 = 6
 =R.H.S
 y *(3*y) = 6
 ∴ y = 4 is satisfied